Fastening structure

Abstract

To provide a fastening structure capable of suppressing change of a friction coefficient to stably provide a small friction coefficient.SOLUTION: A fastening structure is configured to fasten a plurality of components together by screwing a bolt and a nut or the components. In at least a part of a contact area between the bolt and the nut or the components and a contact area between the nut and the components, the bolt or the nut is coated with an alumina thin film formed by the atomic layer deposition method.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a fastening structure.

Background Art

[0002] For fastening a plurality of components formed of metal such as vehicle body parts and aircraft parts, a fastening structure is adopted in which a male screw of a bolt is passed through a through hole of a component and screwed into a female screw of a nut. Since the bolt and the nut are made of metal such as stainless steel, nickel, and nickel alloy, seizure is likely to occur between the bolt and the nut due to friction therebetween. Therefore, in order to suppress the occurrence of seizure between the bolt and the nut, the surfaces of the bolt and the nut are treated to reduce the frictional resistance.

[0003] As a fastening structure subjected to a treatment for reducing the frictional resistance, for example, a fastening member is disclosed in which the surface of a fastening portion is coated with a friction coefficient stabilizer composed of an aqueous liquid containing a polyolefin wax emulsion and a urethane-modified polyolefin emulsion or an olefin-unsaturated carboxylic acid copolymer emulsion (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the fastening member of Patent Document 1, since the friction coefficient stabilizer is composed of a resin component, the heat resistance temperature of the friction coefficient stabilizer is not high. Therefore, when the fastening member is exposed to a high temperature (for example, 100°C to 150°C), there is a problem that the characteristics of the friction coefficient stabilizer change, resulting in a decrease in the friction coefficient and an inability to exhibit an appropriate friction coefficient.

[0006] One aspect of the present invention aims to provide a fastening structure that can suppress changes in the friction coefficient and stably have a small friction coefficient.

Means for Solving the Problems

[0007] One aspect of the fastening structure according to the present invention is a fastening structure for fastening a plurality of the components to each other by screwing a bolt and a nut or a component, wherein at least a part of the contact area between the bolt and the nut or the component and the contact area between the nut and the component, the bolt or the nut is coated with an alumina thin film formed by atomic layer deposition.

Effects of the Invention

[0008] One aspect of the fastening structure according to the present invention can suppress changes in the friction coefficient and stably have a small friction coefficient.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described in detail. For ease of understanding the description, the same reference numerals are assigned to the same components in each drawing, and redundant descriptions are omitted. Also, the scales of the respective members in the drawings may be different from the actual ones. In this specification, "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value, unless otherwise specified.

[0011] A fastening structure according to an embodiment of the present invention will be described. The fastening structure according to this embodiment is a fastening structure for fastening a plurality of components to each other by screwing one fastening member, a bolt (screw), and the other fastening member, a nut or one or more components, and at least a part of the contact area between the bolt and the nut or component and the contact area between the nut and the component is coated with an alumina thin film formed by atomic layer deposition (ALD: Atomic Layer Deposition).

[0012] FIG. 1 is a side view schematically showing a fastening structure according to an embodiment of the present invention, FIG. 2 is a side view showing a disassembled state of the fastening structure of FIG. 1, and FIG. 3 is a cross-sectional view showing a disassembled state of the fastening structure of FIG. 1. In FIGS. 1 to 3, a form in which a bolt and a nut constituting the fastening structure according to this embodiment are screwed together to fasten two components will be described.

[0013] As shown in FIGS. 1 and 2, the fastening structure 1 according to this embodiment includes a bolt 10, a nut 20, and an alumina thin film 30, and two components 2 and 3 may be fastened by screwing the bolt 10 and the nut 20 together.

[0014] Note that the dashed-dotted line in FIGS. 1 to 3 indicates the central axis J of the fastening structure 1. The central axis J is an axis that is the center of the fastening structure 1 when the bolt 10 and the nut 20 are screwed together.

[0015] As shown in FIGS. 1 and 2, the bolt 10 is a hexagonal bolt with a flange that is inserted into the bolt holes 2A and 3A of the components 2 and 3, and has a head 11 and a shaft portion 12.

[0016] The head 11 has a base body 111 and a flange portion 112.

[0017] The base body 111 is a columnar member and is formed in a substantially hexagonal shape in plan view. The shape of the base body 111 in plan view is not particularly limited, and may be a polygon such as a substantially triangular shape, a substantially quadrangular shape, or a circular shape.

[0018] The flange portion 112 is a disk-shaped member and is provided on one end face (the lower end face in FIGS. 1 to 3) of the base body 111. The flange portion 112 is formed to have a larger diameter than the base body 111.

[0019] The shaft portion 12 extends from the head 11 so as to be substantially perpendicular to the back surface of the head 11. The shaft portion 12 is formed in a columnar shape and has a male screw (external screw) 121 formed on the tip end portion 12a to a midway portion thereof so as to be screwable into the female screw (internal screw) 20a of the nut 20.

[0020] The base body 111, the flange portion 112, and the shaft portion 12 may be integrally formed, or may be formed by joining with welding, an adhesive, or the like.

[0021] As shown in FIGS. 1 and 2, the nut 20 is a hexagonal nut with a flange that is tightened to the male screw 121 of the bolt 10 while sandwiching the components 2 and 3, and has a nut body 21 and a flange portion 22.

[0022] The nut body 21 is a columnar member similar to the base body 111 of the head 11 and is formed in a substantially hexagonal shape in plan view. The shape of the nut body 21 in plan view is not particularly limited, and may be a polygon such as a substantially triangular shape, a substantially quadrangular shape, or a circular shape.

[0023] The flange portion 22 is formed on one end face (the upper end face in FIGS. 1 to 3) of the nut body 21 and is formed to have a larger diameter than the nut body 21.

[0024] As shown in Fig. 3, the nut 20 has an internal thread 20a on the wall surface of its through hole, which is threaded with the external thread 121 of the bolt 10. The internal thread 20a includes an internal thread 21a provided on the wall surface of the through hole of the nut body 21 and an internal thread 22a provided on the wall surface of the through hole of the flange portion 22.

[0025] As materials for forming the bolt 10 and the nut 20, metals such as steel, stainless steel, titanium, nickel, nickel alloy, aluminum, aluminum alloy, brass, etc. can be used.

[0026] Part or all of the bolt 10 and the nut 20 may be surface-treated. As the surface treatment, for example, plating treatment, phosphating treatment, black dyeing treatment, metal infiltration treatment, zinc-chromium treatment, trivalent chromium chemical conversion coating treatment (trivalent chromate treatment), etc. can be used.

[0027] The alumina thin film 30 may be provided so as to cover at least a part of the bolt 10 or the nut 20 in the contact region where the bolt 10 and the nut 20 contact each other, the contact region where the bolt 10 and the component 2 contact each other, and the contact region where the nut 20 and the component 3 contact each other.

[0028] In this embodiment, the contact regions are four regions: one end face (the lower end face in Figs. 1 - 3) 112a of the flange portion 112, the external thread 121 of the shaft portion 12, the internal thread 20a of the nut 20, and one end face (the upper end face in Figs. 1 - 3) 22b of the flange portion 22. As shown in Fig. 3, the alumina thin film 30 may be provided in these four regions. Note that the alumina thin film 30 may be provided in any one of these four regions, or may be provided in 1 to 3 of these four regions.

[0029] The alumina thin film 30 is formed by the ALD method. The ALD method is one of the vacuum film formation techniques. By utilizing the self-control property of atoms, a gas-phase raw material is exposed to at least a part of the above-mentioned contact region of the bolt 10 or the nut 20 to be deposited, and a thin film is formed layer by layer of atoms. The ALD method can form a film with a higher coating rate than other common film formation methods such as the chemical vapor deposition (CVD) method. Therefore, the alumina thin film 30 can coat at least a part of the above-mentioned contact region of the bolt 10 or the nut 20 with a substantially uniform film thickness along their shapes.

[0030] Also, since the ALD method can form a film layer by layer of atoms, defects such as cracks and defects are less likely to occur in the alumina thin film 30 formed by the ALD method, and particles such as particles are less likely to adhere to the inside or surface of the alumina thin film 30. Therefore, the alumina thin film 30 can have fewer film defects compared to when formed by other common film formation methods.

[0031] Furthermore, since the ALD method is a film formation method using surface reaction, the film thickness can be controlled, for example, to several nm to several tens of nm for film formation. Therefore, even if the alumina thin film 30 is a thin film with a film thickness of, for example, 3.5 nm, the alumina thin film 30 can surely coat at least a part of the above-mentioned contact region of the bolt 10 or the nut 20 with a substantially uniform film thickness.

[0032] By being formed by the ALD method, the alumina thin film 30 can coat the above-mentioned contact region of the bolt 10 or the nut 20 with a substantially uniform film thickness, so that the intrusion of moisture and oxygen from the outside can be suppressed, and the deterioration of the components 2 and 3 can be suppressed.

[0033] The film thickness of the alumina thin film 30 is preferably 100 nm or less, more preferably 1 nm to 35 nm, and even more preferably 3.5 nm to 30 nm. If the film thickness of the alumina thin film 30 is 100 nm or less, the alumina thin film 30 can exhibit the effect of reducing the friction coefficient on its surface. If the film thickness of the alumina thin film 30 is 1 nm to 35 nm, the friction coefficient of the surface can be reduced, and the peeling from the bolt 10 and the nut 20 can be suppressed.

[0034] In the present specification, the film thickness of the alumina thin film 30 refers to the length in the direction perpendicular to the main surface of the alumina thin film 30. The film thickness of the alumina thin film 30 is, for example, the thickness measured at an arbitrary location in the cross-section of the alumina thin film 30. When several locations are measured at arbitrary locations in the cross-section of the alumina thin film 30, it may be the average value of the thicknesses at these measurement locations.

[0035] FIG. 4 is a diagram showing the relationship between the sliding distance and the friction coefficient when a slip test of the fastening structure is carried out by changing the film thickness of the alumina thin film. Note that SUS304 is used as the base material on which the alumina thin film is formed, and the friction coefficient is measured using a reciprocating sliding tester while reciprocating a sphere (ball) in one direction on the base material on which the alumina thin film is formed. The load of the sphere is 8.6 N, the surface pressure is 934 MPa, the moving speed of the sphere is 33 mm / second, the maximum sliding distance when the sphere is reciprocated in one direction is 500 mm, the measurement time of the sliding distance of the sphere is 15 seconds, and the state on the base material on which the alumina thin film is formed is a dry state. The sliding distance in FIG. 4 indicates the sum of the lengths when the sphere is reciprocated on the plate using a reciprocating sliding tester. In FIG. 4, in Example 1, the film thickness of the alumina thin film formed on the base material is 3.5 nm, in Example 2, the film thickness of the alumina thin film formed on the base material is 35 nm, in Example 3, the film thickness of the alumina thin film formed on the base material is 180 nm, and in Example 4, no alumina thin film is formed on the base material.

[0036] As shown in FIG. 4, it was confirmed that when the film thickness of the alumina thin film is 3.5 nm to 35 nm, the friction coefficient can be stably suppressed to about 0.15 or less.

[0037] The variation in the film thickness of the alumina thin film 30 is preferably ±30% or less, more preferably ±25% or less, and even more preferably ±20% or less. If the variation in the film thickness of the alumina thin film 30 is within the above preferred range, the surface uniformity of the alumina thin film 30 is enhanced, and the alumina thin film 30 can more effectively exhibit the effect of reducing the friction coefficient on its surface.

[0038] In this specification, the thickness variation of the alumina thin film 30 may be defined as follows: At several locations at arbitrary positions in the cross-section of the alumina thin film 30, measurements are taken, and the value obtained by multiplying 100 by the difference between the maximum value and the minimum value of the thicknesses at these measurement locations divided by the average value of the thickness of the alumina thin film 30 at the above measurement locations (thickness variation of the alumina thin film 30 (%) = (maximum value of the thickness of the alumina thin film 30 - minimum value of the thickness of the alumina thin film 30) / average value of the thickness of the alumina thin film 30 × 100). Alternatively, the thickness variation of the alumina thin film 30 may be defined as the value obtained by multiplying 100 by the deviation from the average value of the thickness at the above measurement locations of the alumina thin film 30 divided by the average value of the thickness of the alumina thin film 30 (thickness variation of the alumina thin film 30 (%) = (deviation from the average value of the thickness of the alumina thin film 30) / average value of the thickness of the alumina thin film 30 × 100).

[0039] A method for manufacturing the fastening structure 1 will be described. As shown in FIG. 2, first, an alumina thin film 30 is formed on the contact region of the bolt 10 or the nut 20 using the ALD method (alumina thin film forming step).

[0040] As described above, the contact regions are the four regions of one end face 112a of the flange portion 112, the male thread 121 of the shaft portion 12, the female thread 20a of the nut 20, and one end face 22b of the flange portion 22.

[0041] The film formation conditions of the ALD method will be described.

[0042] When forming the alumina thin film 30 using the ALD method, at least a part of the above contact region of the bolt 10 or the nut 20 is exposed, the other parts are covered, and it is installed in the reaction apparatus. Then, as a precursor, a material for forming the alumina thin film 30 is supplied into the reaction apparatus and adhered to at least a part of the above contact region of the bolt 10 or the nut 20.

[0043] As the material for forming the alumina thin film 30, it is preferable to use an aluminum compound. The aluminum compound may be any gas component that contains aluminum and can be vaporized. For example, trimethylaluminum (TMA), triethylaluminum (TEA), trichloroaluminum, dimethylaluminum hydride (DMAH), etc. can be used.

[0044] After attaching the material for forming the alumina thin film 30 to at least a part of the above-mentioned contact area of the bolt 10 or the nut 20, the remaining material for forming the alumina thin film 30 is exhausted from the reaction apparatus. Then, an oxidizing agent is supplied into the reaction apparatus to react with the material for forming the alumina thin film 30 attached to at least a part of the above-mentioned contact area of the bolt 10 or the nut 20 to form alumina.

[0045] The oxidizing agent may be any material that can oxidize the aluminum compound. For example, water vapor, ozone, oxygen radicals excited by plasma, etc. can be used.

[0046] The reaction time in the reaction apparatus is not particularly limited and can be appropriately designed.

[0047] The reaction temperature in the reaction apparatus can be appropriately designed and is preferably 400 °C or lower.

[0048] By forming the alumina thin film 30 under the film formation conditions of the ALD method, even when the alumina thin film 30 is formed on uneven portions such as the male thread 121 of the shaft portion 12 of the bolt 10 and the female thread 20a of the nut 20, the variation in the film thickness of the alumina thin film 30 can be suppressed to ±30% or less.

[0049] Next, the shaft portion 12 of the bolt 10 is inserted into the bolt holes 2A and 3A of the components 2 and 3, and the male thread 121 formed from the tip portion 12a to the middle of the shaft portion 12 is screwed into the female thread 20a of the nut 20, thereby fastening the bolt 10 and the nut 20 (fastening step).

[0050] As a result, a fastening structure 1 is obtained in which the components 2 and 3 are fastened with the bolt 10 and the nut 20.

[0051] In this way, in the fastening structure 1, at least a part of the bolt 10 or the nut 20 in the above contact area is coated with the alumina thin film 30 formed by the ALD method. Since the alumina thin film 30 is formed by the ALD method, the surface of the alumina thin film 30 is smooth and the variation in unevenness can be reduced, so that the friction coefficient can be kept small. Further, even when the fastening structure 1 is placed in a high temperature environment (for example, 100°C to 150°C), the change in the characteristics of the alumina thin film 30 can be suppressed, so that the desired friction coefficient can be stably maintained. Therefore, the fastening structure 1 can suppress the change in the friction coefficient of at least a part of the above contact area of the bolt 10 or the nut 20 and stably have a small friction coefficient. The friction coefficient can be, for example, 0.2 or less, more preferably 0.15 or less.

[0052] In the fastening structure 1, since the bolt 10 and the nut 20 are easily tightened, the axial force required when tightening with a smaller force (torque) can be obtained. In actual fastening work, generally, the management of the axial force is carried out by the magnitude of the torque. In order to obtain a certain axial force with a smaller torque, it is necessary to stably suppress the friction coefficient to be smaller. Since the fastening structure 1 can stably screw the bolt 10 and the nut 20 with a smaller torque when fastening the components 2 and 3 together, the components 2 and 3 can be reliably fastened even with a small torque.

[0053] Note that the friction coefficient refers to the total friction coefficient μ when the bolt 10 and the nut 20 slide due to tightening. The friction coefficient is a value obtained by summing up various friction coefficients occurring in the above contact area of the bolt 10 and the nut 20. The value obtained by summing up various friction coefficients may be a value representing various friction coefficients or a value integrating various friction coefficients. Note that any of the above values obtained by summing up, representing, and integrating are not values obtained by adding up various friction coefficients occurring in the contact area, but may be values obtained by averaging various friction coefficients occurring in the contact area.

[0054] Generally, when bolts and nuts are formed using stainless steel, since stainless steel has a lower thermal conductivity and a higher friction coefficient than carbon steel or the like, galling is likely to occur particularly between the bolt and the nut during fastening. Even when the bolt 10 and the nut 20 are formed using stainless steel, the fastening structure 1 can stably reduce the friction coefficient in these contact areas, so that heat generation in the contact area between the bolt 10 and the nut 20 during fastening can be suppressed. As a result, galling of the bolt 10 and the nut 20 can be made difficult.

[0055] The surfaces of the bolt 10 and the nut 20 may be subjected to trivalent chromate treatment as a rust prevention treatment to form a rust prevention film containing trivalent chromium chromate (chromate). Even if the bolt 10 and the nut 20 have a rust prevention film on their surfaces, the fastening structure 1 has an alumina thin film 30 in the contact area between the bolt 10 and the nut 20, so that the friction coefficient in the contact area can be stably maintained at a small value. Therefore, an axial force required with a smaller torque can be obtained when the bolt 10 and the nut 20 are fastened.

[0056] The fastening structure 1 can make the film thickness of the alumina thin film 30 100 nm or less. If the film thickness of the alumina thin film 30 is 100 nm or less, the friction coefficient of the alumina thin film 30 can be sufficiently suppressed to be small. Therefore, the fastening structure 1 can sufficiently suppress changes in the friction coefficient of at least a part of the contact area of the bolt 10 or the nut 20, so that a small friction coefficient can be more stably obtained.

[0057] The fastening structure 1 can make the variation in the film thickness of the alumina thin film 30 ±30% or less. Thereby, the surface of the alumina thin film 30 can be made smoother and the variation in unevenness can be made smaller, so that the friction coefficient of the alumina thin film 30 can be further suppressed to be small. For this reason, the fastening structure 1 can further suppress changes in the friction coefficient of at least a part of the contact area of the bolt 10 or the nut 20, so that a small friction coefficient can be more stably obtained.

[0058] As described above, even when the fastening structure 1 is exposed to high-temperature conditions, it can suppress the change in the friction coefficient of at least a part of the contact regions of the bolt 10 or the nut 20 and stably have a small friction coefficient. Therefore, the fastening structure 1 can be suitably used for fixing vehicle body parts, aircraft parts, space parts, etc. that are used under high-temperature conditions, such as space-related structures of vehicles, aircraft, artificial satellites, etc.

[0059] In addition, in the present embodiment, the case where the bolt 10 passes through the bolt holes 2A and 3A of the components 2 and 3 and is screwed with the nut 20 has been described. However, female threads may be formed in the bolt holes 2A and 3A of the components 2 and 3, and the bolt 10 may be screwed into the bolt holes 2A and 3A.

[0060] In the present embodiment, as one of the fastening members, instead of the bolt 10, a threaded bolt, an embedded bolt, a tap bolt, etc. may be used. In this case, the bolt holes 2A and 3A of the components 2 and 3 may be female threads. Thereby, the fastening structure 1 according to the present embodiment can be configured by screwing a threaded bolt, an embedded bolt, a tap bolt, etc. with the bolt holes 2A and 3A.

[0061] In the present embodiment, the fastening structure 1 fastens two components 2 and 3, but the number of components may be one or three or more.

[0062] As described above, the embodiments have been described. However, the above embodiments are presented as examples, and the present invention is not limited by the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention and are included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0063] 1 Fastening structure 2, 3 Components 10 volts 11 head 111 base 112, 22 flange part 112a, 22b end face 12 shaft part 121 male screw (external screw) 20 nut 20a, 21a, 22a female screw (internal screw) 21 nut base 30 alumina thin film

Claims

【Claim 1】 A fastening structure for fastening a plurality of said components together by screwing a bolt with a nut or a component, at least a part of said bolt or said nut in a contact area between said bolt and said nut or said component and a contact area between said nut and said component is coated with an alumina thin film formed by atomic layer deposition, the film thickness of said alumina thin film is from 1.0 nm to 3.5 nm, the variation in the film thickness of said alumina thin film is ±25% or less, and a fastening structure in which the friction coefficient of said alumina thin film is 0.15 or less.

Images